Arc torch device



INVENTORS C. ESCHENBACH M. SKINNER M. GAGE ATTORNEY R. C. ESCHENBACH ETAL ARC TORCH DEVICE 2 Sheets-Shea?I 1 RICHARD GEORGE ROBERT Oct. 8, 1963Oct. 8, 1963 R. c. EscHENBAcH ETAL 3,106,632

- f ARC TORCH DEVICE Filed April 2l, 1961 2 Sheets-Sheet 2 INVENTORSRICHARD C. ESCHENBACH GEORGE M. SKINNER ROBERT M. GAGE United StatesPatent .O

3,106,532 ARC TORCH DEVICE Richard C. Eschenbach and George M. Skinner,Indianapoiis, Ind., and Robert M. Gage, Summit, NJ., assignors to UnionCarbide Corporation, a corporation of New York Filed Apr. 21, 1961, Ser.No. 104,575 13 Claims. (Cl. 219-75) The present invention relates to animproved are torch device for heating a gaseous medium such as air. Moreparticularly, it relates to such a device fwlierein extremely hi-ghpower :may be supplied to the arc and -thence to the gaseous medium.

There is an increasing need in industry for apparatus that will produceenvironmental conditions for certain research and tests on a scaledldown or laboratory basis. In certain instances, :such conditions havebeen virtually non-reproducible on such a laboratory basis. In theaviation, missile and space exploration fields, for example, equipmentis desired 'which will produce gas velocities far exceeding the speed ofsound vand/or temperatures far exceeding the melting points of mostknown materials. Devices capable of producing such gas velocities andtemperatures on a laboratory basis are largely unobtainable. Theadvantages to be gained from such a device are obvious in terms ofmaking it possible to pretest airframe shapes, material durability atelevated temperatures and fthe like. Such pretesting is, of course,necessary 'to the protection of human life and the successful operationand recovery of extremely expensive unmanned vehicles.

High velocity, high temperature air streams are desired for wind tunnelsand other materials testing devices. In such devices high gas velocitiesand tempera tures are required.

Electric arcs are essentially high temperature devices and have beenused for many years as cutting torches, for plating processes, for`cr-acking hydrocarbons in the production of acetylene, and othersimilar uses. Of recent years, these arc .devices have become useful inVarious high temperature gas hea-ting applications. In suchapplications, it is of prime importance to supply a maximum amount ofpower to the arc and then to transfer such power to the gas effluent. Ithas been found that if higher power to an arc device lis achieved solelythrough current increases, suoli additional power is used up primarilyin heating the electrodes and their cooling fluid streams. Voltageincreases, on the other hand, are substantially completely transmittedas higher heat to the arc gas.

Novel method and apparatus tor providing the above hot Iair streams aredescribed in copending U.S. Patent Application Serial No. 716,323, tiledon February 20, 1958, by R. M. Gage et al, lnow U.S. Patent 3,077,108.This prior method comprises striking an arc between a stick electrodeand a nozzle anode having a divergent outlet passage. In one form ofapparatus for carrying out this method the stick cathode, usually ofthoriated tungsten, is protected from air oxidation by means of asurrounding protective sleeve which extends in length .at least to thetip `ot the stick cathode. A shielding gas stream passes through theannulus between the protective sleeve and the cathode while an airstream travels along the exterior of the protective sleeve.

At power input levels iabove about 40 kw., the above described apparatusunde` goes severe damage at several points. First, the protective sleevesuffers erosion which enables air to reach the hot tungsten cathode anddamage it by oxidation. Second, flow relationships between the shieldinggas and air streams are such as to lead at mize chemical attack by thefi, i ,tifii Fatented Oct. 8, 1963 zle due to the sleeve becoming quitehot. This double arcing also contributes to sleeve erosion. The erosionand damage of the apparatus contaminates the elfluent and disturbsproper test conditions.

Novel apparatus has now been developed which enables power input up toat least kw. to be used without appreciable equipment damage andcontamination or the effluent. The present invention is an improvementover the disclosure of the `above mentioned Serial No. 716,323.

it is laccordingly the primary object of this invention to provide anelectric arc gas heating device capable of handling large amounts ofpower Iand of transferring a large percentage of such power to the gas.

Other objects are to provide apparatus for obtaining maximum heattransfer to the gas; and to provide appara-tus for use at power levelsof at least about 100 kw.

Other objects will be pointed out or become apparent from the followingdetailed description and drawings wherein:

FIGURE 1 is a cross-sectional view of the present invention;

FIGURE 2 is a cross-sectional view of the apparatus of the inventiontogether with a hypersonic wind tunnel.

The torch to be described herein preferably operates in awall-stabilized -mode such as is described in U.S. 2,858,411, issuedOctober 28, 1958, to R. M. Gage.

As shown in FIGURE l, the device consists mainly of a torch body 16, aninner electrode 11, the shape of which forms an angle of 60 at its tipin order to minigas flowing through the torch and which is preferablymade of thoria-ted tungsten, and la replaceable non-consumable nozzleelectrode 12, preferably made of metal such as copper. Other nozzlematerials such as silver, tungsten, molybdenum and aluminum can also beused if desired. The stick cathode is supported by collet 13. The nozzleanode is held in position by vvater jacket 14. The jacket 14 is composedof sleeve 14a and outer jacket Mb which are silver brazed together toeffectively form a single unit. The jacket 14 screws into insulator l15which, in turn, is held in position by insulator nut 16. The stickelectrode preferably has a diameter of from 1/8 to 2%4 inch in order toinsure that it has sufficient current carrying capacity without havingan excessive amount of material. The nozzle has a throat section thediameter of ywhich is preferably between Ms and We inch in order toinsure that for a given pressure the arc will be maintained within thenozzle in a stable condition.

The nozzle 12 is kept from melting during operation by improved watercooling. The water enters the cooling jacket 14 through inlet 17, passesrapidly through cooling annulus 18, then out through outlet 19. Leakage`of cooling water is prevented by Orings 2d, 21, and 2.2. In Iorder toprovide maximum cooling and prevent melting of the nozzle interior, theratio of the OD. of the nozzle to its LD. at its point of smallest crosssection should be between 2.0 and `12.0. -Optimumly, when the nozzleinternal diameter is about 1A 4inch at its point of smallestcross-section, the O.D.to-I.D. ratio of the nozzle is between 2.2 and4.2. For a nozzle internal dia-meter of 1/s inch, the O.D.tc-I.D. ratioshould be about 3.0 to 8.0 while a nozzle internal diameter of inchshould have an GData-ID. ratio of about 2 to 4. The water coolingpassage surrounding the nozzle cuter surface is made relatively thin inorder to 4increase the velocity of the cooling medium in direct Contactwith the nozzle electrode.

l5-90' and preferably about 60.

In contrast to the above 0.D.-to-I.D. data, the prior Serial No. 716,323discloses use of nozzle anodes having .an O.D.-tol.D. ratio of 20 for1/16 inch internal diameter nozzles and 4 for 1/z inch diameter nozzles.

Shielding gas, such as argon, under pressure enters through inlet 23passes down along cathode 1l, through annulus 2d between cathode 11 andprotective sleeve 25, then passes out through orifice 26 in nozzle anode12. The passage 126 has a divergent section 27. Annul-us 24 must be atan optimum size to insure proper shielding of the tungsten cathode l1with a minimum amount of shielding gas to minimize dilution of the gasto be heated. Specifically, the annulus must be small enough to achieveshielding gas velocities of fnom about 20 ft./sec. to 200 ft./sec. andyet be large enough to i-nsure a uniform flow of gas. An annulus widthtof 0.031 inch with a shielding gas velocity of about 90 t/ sec. ispreferred. However, the annulus width may have any -value in the rangeof tfrom about 1/64 to about 1/16.

Protective slee-ve 25 has improved -water cooling passages which preventit from -melting and eroding during operation. Cooling water entersthrough :inlet 28, passes through conduit 29, annular passage 3:0,whereby cooling is imparted to the tip of the protective sleeve, passesout through conduit 31 and youtlet 32 by way of passage 32a. Thisimproved sleeve cooling tends to prevent double arcing from cathode tosleeve to nozzle anode and thus reduces sleeve erosion due to mel-ting.

An additional feature of the protective sleeve 25 is the plated tip 38of the sleeve. This plated portion is approxi mately .010 inch inthickness and consists of a pure aluminum oxide. Such plated portionalso tends to reduce sleeve erosion due to melting caused by doublearcing.

The tip of the stick cathode is preferably made flush with the tip ofthe protective sleeve 25. lf it is allowed to n project beyond the tipof the sleeve it will be subjected to the erosive effects of thesurrounding air stream. On the other hand, if it is set back from thetip of the sleeve, the sleeve will become too hot and melt down.

The arc is further prevented from wandering `from the stick cathode toother parts yof the device other than the nozzle anode by insulators 15and 39. Suitable materials for the insulators have been found to beBakelite, Formica and nylon.

Air under pressure enters through inlet 33 and passes through annularpasage 34 between protective sleeve 25 and insulator l plus nozzle 12.This annular passage should be properly dimensioned in lorder to providea streamlined air flow approaching the throat 35 in nozzle 12. Thisminimizes the turbulence in the area directly in front of the tip ofcathode 11 and minimizes erosion of the cathode tip andthe nozzlethroat. Generally, passage 35 should have a length of from 1/2 inch to 2inches and preferably a length of 1% inches. Its width should be between1/32 to 1A; inch. However, in choosing any one length-width combination,care must be taken to maintain a length-to-width ratio of the passage ofat least 1'5 and preferably between 20`25 so that the desiredstreamlined flow can be insured. To further insure a streamlined flow,the passage should have an included angle of from The air then mixeswith the shielding gas las they both pass out through passage 35 andorifice 26 in nozzle l2. This description of the apparatus impl-.iesaxial gas ilo-w. Alternatively, the main gas stream could be introducedto annular passage 34 in a tangential fashion to produce a vortex gasflow through nozzle passages 35 and 27.

Nozzle erosion has been additionally minimized by maintaining alengthtodiameter ratio in the throat section 35 of between 0.5 and 2.0.The heat concentration :is highest in the throat section 35. lf thelength of the throat is too short when the first bit of erosion occursthe high heat concentration becomes aggravated because the throat tendsto become a point. On the other hand, if the throat is too long the arcwill terminate in the throat. The included angle of the :divergentportion Z7 of passage 26 should be less than 20 degrees and its lengthsix times the throat diameter and preferably between 3A and l1/z inchesso that the arc from electrode lll. terminates well within the nozzleunder desired operation conditions. lf the angle is too large thepressure within the nozzle will become excessive causing the arc tolocate at a point. On the other hand, if the angle is small enough, thepressure will be low enough to allow the arc to spread but within thenozzle.

The tip 3o of cathode 1l and the rim 37 of protective sleeve 25 aremaintained at a controlled ldista-nce or setback from the ,mouth of thenozzle throat section 35. This helps to minimize turbulence 4and erosionin this area. For a cathode having a diameter from 1/s to 2%4 inch and anozzle having la throat diameter from Ms to s/8 v inch, this set-backdistance should be lfrom W32 to l inch. With an 1%4 inch cathode and a1/s inch diameter throat and a set-back of %2, it was found that avariation in setback distance of /l inch increased erosion of theprotective sleeve and stick cathode.

In operation, an electrical power source (not shown) is connectedbetween stick cathode l1 and nozzle anode l2, and the arc isconveniently initiated by pushing electrode 11 down into arcing relationto nozzle electrode l2, then retracting it to the desired operatingposition. Direct current straight polarity is the preferred type ofcurrent for this device. Alternating current could also be used. Thecombined air-shielding gas streams force the arc down into the nozzlepassage 26, where the arc becomes wall-stabilized along the so-includedportion. The gases passing through this high intensity wallstablized arcare heated to desired energy content and are discharged in a supersonichot jet.

The material or body to be tested is located at point X in the hot aireffluent that is discharged from the device. For example, in FlGURE 2,there is depicted a hypersonic wind tunnel 5@ connected to the describedarc air heater 10 for testing aircraft materials at hypersonicvelocities. The hot air effluent coming from the torch body 10 isexpanded through expansion section 51 and then directed against thematerial to be tested at 52. By connecting a suitable vacuum pump to theexit of the iiow section 53, a desired pressure drop can be obtainedbetween the flow section and the expansion section to yield the desiredvelocities. Testing is thereby accomplished under conditions thatclosely simulate conditions of actual ilight of such body or material.

In the following example of the operation of the present novel device,apparatus of the type depicted in FGURE 1 was used.

In this example an arc of 355 volts (D.C. SP.) and 400 amperes wasmaintained between a 3/16 diameter thoriated tungsten stick cathode anda nozzle anode having a divergent orifice section expanding from adiameter of 9&2 to a diameter of 15/32. The nozzle had an outer diameterof 1%. Argon shielding gas at 800 c.f.h. and air at 7600 c.f.h. passedseparately into the apparatus and then mixed while passing out throughthe nozzle anode orifice. Under these conditions the total powerdeveloped was 142 kw. of which 122 kw. went to the gas to yield anenthalpy of 750 Btu/lb. The hot air eiuent discharging from a chamberpressure of 224 p.s.i.g. through the nozzle had a calculated exitvelocity of 4500 ft./sec. at a calculated exit pressure of 23 p.s.i.a.,which is approximately Mach 2.1 for these conditions.

While air and argon gas are given above by way of example, it will beunderstood that other reactive gases, such as carbon dioxide, oxygen,and iiuorine, may be used in admixture with or in place of air, andother gases inert relative to the cathode, such as helium, hydrogen,krypton, neon, nitrogen, xenon, carbon monoxide, and mixtures thereof,may be used in admixture with or in place of argon. Also, the latter maybe used in admixture with or in place of air without departing from thebasic concept of the invention.

As can be seen by the drawing and as is apparent from the description ofthe apparatus, the internal parts of the torch, such as the innerelectrode, the nozzle electrode, and the protective sleeve, are easilyreplaceable.

in summary, the present invention consists of an improvednon-transferred arc torch which is capable of operating at power levelsat least as high as 100 kw. with an air stream passing through thenozzle without appreciable damage to the stick cathode, protectivesleeve, or nozzle anode.

What is claimed is:

1. An electric arc gas heater device comprising the combination of astick electrode, a replaceable protective sleeve surrounding the arc endof said electrode and electrically isolated from said electrode inspaced concentric relation, means for delivering a shielding gas to theannular space between said sleeve and stick electrode which isdischarged `from said sleeve about such end of said electrode to protectsuch arc end, a replaceable cooled non-consumable nozzle electrodehaving an internal conical gas passage surrounding the end of saidsleeve in spaced concentric relation, means for delivering gas underpressure to said conical passage for ilow about such end of said sleeve,said nozzle having a gas outlet comprising a throat leading to anexpansion passage of increasing diameter for the expansion of such gasas it is discharged therefrom, means for striking a high-pressure arcbetween said nozzle and the arc end of said stick electrode for heatingthe gas discharged by said nozzle, insulator means surounding at leastpart of said sleeve and cooperatingy with the walls of said nozzleelectrode defining said internal conical gas passage to form an annularpassage with said sleeve, said annular passage having a length-towidthratio of at least about 15, and means for providing a cooling medium indirect contact with said protective sleeve, whereby cooling is impartedto the end of said protective sleeve such that said arc torch maydeliver up to about 100 kw. Without damage to said torch.

2. Apparatus according to claim 1 wherein said protective sleeve isprovided with a plated tip, the thickness of said plating beingapproximately .010 inch and consists of a pure aluminum oxide.

3. Apparatus according to claim 1 wherein the lengthto-diameter ratio ofsaid throat section is between about 0.5 and 2.0 and the included angleof said increasing diameter expansion passage is less than 20 degrees.

4. Apparatus according to claim 3 wherein said ininciuded angle isbetween about 5 to 10 degrees.

5. Apparatus according to claim 1 wherein said annular passage has alength-to-width ratio of between about 20 and 25.

6. Apparatus according to claim 1 wherein said stick electrode has adiameter of from s to 2%4 inch; said throat has a diameter or from 1/sto inch and said cathode is set back from said throat section from about5)/32 inch to 1 inch.

7. Apparatus according to claim l wherein said nozzle anode has anO.D.to.l.D. ratio of from about 2.2 to about 4.2 when the internaldiameter thereof at the point of smallest cross section is about M1,inch.

8. Apparatus according to claim 1 wherein said nozzle anode has anCLD-toil). ratio of from about 3 to about 8 when the internal diameterthereof at the point of smallest cross section is about 1%; inch.

9. Apparatus according to claim 1 wherein said nozzle anode has anO.D.to-I.D. ratio of from about 2 [to about 4 when the internal diameterthereoiT` at the point of smallest cross section is about inch.

l0. Apparatus according to claim l nuiar space has a 1/16 inch.

1l. Apparatus according to claim `1 wherein said annular space has awid-"h of about .031 inch.

12. Apparatus according to claim 1 wherein said nozzie electrode has anO.D.-tol.D. ratio of from about 2.0 to about 12.0.

13. Apparatus according to claim 1 wherein said nozzle electrode isnon-consumable and in which at least a portion of said arc iswall-stabilized.

wherein said anwidth of from about 1&4 inch to about References CCitedin the tile of this patent UNITED STATES PATENTS 1,002,721 Mathers Sept.5, 1911 2,093,821 Southgate Sept. 21, v1937 2,616,017 Anderson Oct. 28,1952 2,890,322 Oylcr et al June 9, 1959

1. AN ELECTRIC ARC GAS HEATER DEVICE COMPRISING THE COMBINATION OF ASTICK ELECTRODE, A REPLACEABLE PROTECTIVE SLEEVE SURROUNDING THE ARC ENDOF SAID ELECTRODE AND ELECTRICALLY ISOLATED FROM SAID ELECTRODE INSPACED CONCENTRIC RELATION, MEANS FOR DELIVERING A SHIELDING GAS TO THEANNULAR SPACE BETWEEN SAID SLEEVE AND STICK ELECTRODE WHICH ISDISCHARGED FROM SAID SLEEVE ABOUT SUCH END OF SAID ELECTRODE TO PROTECTSUCH ARC END, A REPLACEABLE COOLED NON-CONSUMABLE NOZZLE ELECTRODEHAVING AN INTERNAL CONICAL GAS PASSAGE SURROUNDING THE END OF SAIDSLEEVE IN SPACED CONCENTRIC RELATION, MEANS FOR DELIVERING GAS UNDERPRESSURE TO SAID CONICAL PASSAGE FOR FLOW ABOUT SUCH END OF SAID SLEEVE,SAID NOZZLE HAVING A GAS OUTLET COMPRISING A THROAT LEADING TO ANEXPANSION PASSAGE OF INCREASING DIAMETER FOR THE EXPANSION OF SUCH GASIT IS DISCHARGED THEREFROM, MEANS FOR STRIKING A HIGH-PRESSURE ARCBETWEEN SAID NOZZLE AND THE ARC END OF SAID STICK ELECTRODE FOR HEATINGTHE GAS DISCHARGED BY SAID NOZZLE, INSULATOR MEANS SURROUNDING AT LEASTPART OF SAID SLEEVE AND COOPERATING WITH THE WALLS OF SAID NOZZLEELECTRODE DEFINING SAID INTERNAL CONICAL GAS PASSAGE TO FORM AN ANNULARPASSAGE WITH SAID SLEEVE, SAID ANNULAR PASSAGE HAVING A LENGTH-TOWIDTHRATIO OF AT LEAST ABOUT 15, AND MEANS FOR PROVIDING A COOLING MEDIUM INDIRECT CONTACT WITH SAID PROTECTIVE SLEEVE, WHEREBY COOLING IS IMPARTEDTO THE END OF SAID PROTECTIVE SLEEVE SUCH THAT SAID ARC TORCH MAYDELIVER UP TO ABOUT 100 KW. WITHOUT DAMAGE TO SAID TORCH.